FIG. 1 is a cross-sectional view of a conventional image intensifier tube, generally designated as 10. As shown, image intensifier tube 10 includes a cathode plate, generally designated as 11, microchannel plate (MCP) 12, and a fiber optic anode plate, generally designated as 13. Light enters cathode plate 11 and is guided through a window striking a photocathode 15. Due to photoelectric conversion, electrons are emitted from photocathode 15. The electrons exiting from cathode plate 11 are amplified by MCP 12. These electrons are accelerated and caused to impinge on phosphor face 14 of fiber optic anode plate 13, thereby emitting fluorescent light. The emitted light is guided through fiber optic anode plate 13, by way of multiple fibers 16, so as to yield output light.
Although not shown, the exiting light from fiber optic anode plate 13 may be coupled to a charge coupled device (CCD) by way of a tapered fiber optic bundle. As shown in FIG. 1, photocathode 15, MCP 12 and phosphor face 14 are contained within a vacuum formed by housing 17.
It will be appreciated that image intensifier tube 10 is not drawn to scale. More specifically, multiple fibers 16, in the fiber optic anode plate are not drawn to scale. There are typically millions of fibers 16, in the anode plate.
FIG. 2A shows an individual fiber 20, representing each of multiple fibers 16 in fiber optic anode plate 13, which may or may not be of the same materials or dimensions. Fiber 20 includes glass rod 22 and glass cladding 21, which surrounds the glass rod. The glass material of cladding 21 is different from the glass material of rod 22.
Optical fiber 20 is formed in the following manner: A glass rod and a cladding tube, coaxially surrounding the glass rod, are suspended vertically in a furnace. The temperature of the furnace is elevated to the softening temperature of the glass. The rod and cladding tube fuse together into single fiber 20. The fiber 20 is fed into a traction mechanism, where the speed is adjusted until a desired fiber diameter is achieved. The fiber is then cut into shorter lengths.
Several thousands of the cut single fiber 20 are then stacked into a mold and heated to a softening temperature of the glass, in order to form an array 25, as shown in FIG. 2B. The array 25 is also known as a multi assembly or a bundle and includes several thousand single fibers 20, each having a glass rod and a cladding tube. The multi assembly 25 is suspended vertically in a drawing machine and drawn to decrease the fiber diameter, while still maintaining the configuration of the individual fibers. The multi assembly 25 is then cut into shorter lengths of bundles.
Several hundreds of the cut bundles 20 are then stacked and packed together into a large diameter glass tube (not shown). After stacking and packing the bundles, the entire assembly is heated and fused together. In this manner, active areas of the fiber optic anode plate are formed from the millions of individual fibers 20.